feat: Generate Debian packages with CPack (#2282)

Builds the Linux packages with CPack. 
Generate them by running Conan with `--options:host "&:package=True"
--options:host "&:static=True"` then after the build you can run `cpack
.` in the build directory.

@mathbunnyru Where do you think this should be built? QA needs a package
per-commit.

@godexsoft What to do with the `config.json` and service file. I can
just remove them or strip the comment out but it still won't work out
the box with the default `rippled.cfg`. Relates to #2191.

---------

Co-authored-by: Ayaz Salikhov <mathbunnyru@users.noreply.github.com>

cmake/pkg/postinst

@@ -0,0 +1,46 @@
+#!/bin/sh
+
+set -e
+
+USER_NAME=clio
+GROUP_NAME="${USER_NAME}"
+CLIO_EXECUTABLE="clio_server"
+CLIO_PREFIX="/opt/clio"
+CLIO_BIN="$CLIO_PREFIX/bin/${CLIO_EXECUTABLE}"
+CLIO_CONFIG="$CLIO_PREFIX/etc/config.json"
+
+case "$1" in
+    configure)
+        if ! id -u "$USER_NAME" >/dev/null 2>&1; then
+            # Users who should not have a home directory should have their home directory set to /nonexistent
+            # https://www.debian.org/doc/debian-policy/ch-opersys.html#non-existent-home-directories
+            useradd \
+                --system \
+                --home-dir /nonexistent \
+                --no-create-home \
+                --shell /usr/sbin/nologin \
+                --comment "system user for ${CLIO_EXECUTABLE}" \
+                --user-group \
+                ${USER_NAME}
+        fi
+
+        install -d -o "$USER_NAME" -g "$GROUP_NAME" /var/log/clio
+
+        if [ -f "$CLIO_CONFIG" ]; then
+            chown "$USER_NAME:$GROUP_NAME" "$CLIO_CONFIG"
+        fi
+
+        chown -R "$USER_NAME:$GROUP_NAME" "$CLIO_PREFIX"
+
+        ln -sf "$CLIO_BIN" "/usr/bin/${CLIO_EXECUTABLE}"
+
+        ;;
+    abort-upgrade|abort-remove|abort-deconfigure)
+        ;;
+    *)
+        echo "postinst called with unknown argument \`$1'" >&2
+        exit 1
+        ;;
+esac
+
+exit 0